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Your BSCI and CCNP exam success relies upon on realizing the facts, and one this sort of detail is recognizing the right way to summarize routes in OSPF. Route summarization is not just a exam of your binary conversion capabilities, but knowing wherever and when to summarize routes. It will not surprise any CCNA or CCNP certification candidate that OSPF offers us the most alternatives for route summarization, and as a result far more facts to know!

OSPF offers us two selections for route summarization configurations. In a preceding tutorial, we seemed at the "summary-deal with" command, and today we'll glance at the suitable use of the "region variety" command.

The "area variety" command need to be utilised on an Region Border Router (ABR) to summarize routes staying advertised from 1 OSPF area to yet another. In this tutorial, R1 is acting as an ABR, with interfaces in both equally Spot and Spot one. 4 loopbacks have been positioned into R1's Spot one.

R1(config)router ospf one

R1(config-router)network twelve... .255.255.255 a 1

R1(config-router)network thirteen... .255.255.255 a one

R1(config-router)network 14... .255.255.255 a 1

R1(config-router)network fifteen... .255.255.255 a 1

The routing table of an OSPF neighbor, R2, displays all 4 routes.

R2show ip route ospf

12.../32 is subnetted, one subnets

O IA twelve.twelve.12.twelve one hundred ten/65 by way of 172.12.123.1, 001852, Serial0

thirteen.../32 is subnetted, one subnets

O IA 13.thirteen.13.13 110/sixty five by way of 172.twelve.123.one, 001842, Serial0

14.../32 is subnetted, one subnets

O IA 14.14.14.14 one hundred ten/sixty five by way of 172.twelve.123.1, 001832, Serial0

fifteen.../32 is subnetted, 1 subnets

O IA 15.fifteen.fifteen.fifteen 110/sixty five by means of 172.twelve.123.one, 001832, Serial0

To retain the routing tables of downstream routers smaller sized but even now have the desired IP connectivity, we can use the spot range command on R1 to summarize these 4 routes. The essential to maintain in thoughts with the area variety command is that the spot quantity offered in the command is the spot containing the locations, NOT the spot that will receive the summary route.

R1(config)router ospf 1

R1(config-router)location 1 range twelve... 252...

R2 now shows a solitary summary route that can be utilized to reach all four remote networks.

R2show ip route ospf

O IA twelve.../6 one hundred ten/sixty five through 172.12.123.1, 000021, Serial0

Curiously adequate, there's now an additional route in R1's routing table.

R1show ip route ospf

O twelve.../6 is a summary, 000753, Null0

When you configure summary routes in OSPF, a route to null0 will be mounted into the OSPF routing table of the router performing the summarization. This assists to protect against routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table, and packets that do not match a single of the summarized routes but do match the summary route will be dropped.